This invention relates to a coffee or tea maker having a freshwater receptacle and a continuous flow heater which is arranged underneath the freshwater receptacle and which is connected therewith by a freshwater intake. The continuous flow heater has an outlet which continues in a riser for the heated water. The continuous flow heater is automatically controlled (energized and de-energized) by a switching arrangement.
Various devices are known for the automatic control of the continuous flow heater of coffee or tea makers.
One type of known control device--also designated as a level control--essentially comprises a pressure-responsive box having an integrated microswitch which turns the continuous flow heater on and off dependent upon the freshwater level.
The above-outlined known control is very accurate, because the control diaphragm of the pressure-responsive box responds in a very sensitive manner. Such a control device, however, is disadvantageous because it is relatively expensive and further, there is a significant risk of soiling the mechanically moved components because these, at least in part, directly contact the fresh water.
Another known control device for the continuous flow heater of a coffee or tea maker includes a so-called bimetal spring (thermostat) switch which, in the known tea or coffee makers is arranged directly at the continuous flow heater and responds to changes of the external temperature of the continuous flow heater. In the entirely switched-off state of the apparatus the bimetal switch is in its closed position, consequently, subsequent to filling the receptacle with fresh water and switching on the apparatus, the brewing process is promptly initiated. Upon reaching a predetermined maximum temperature, the bimetal switch opens and is closed only after the temperature has dropped under a predetermined magnitude.
A bimetal switch of the above-outlined type has the advantage of very low cost. Its use in devices known heretofore is, however, disadvantageous in that the continuous flow heater, because of its relatively large mass, transmits temperature changes only very slowly to the bimetal switch so that the latter very frequently is in its closed position for a much longer period than desirable for the proper functioning of the apparatus. As a result, the continuous flow heater is in an energized state for a relatively long period even at times when only a small volume of residual water dwells in the continuous flow heater.